The long-term GOAL of this research is to elucidate the molecular modulation of ion transport processes in the conjunctiva. This research is built upon our encouraging preliminary finding that the pigmented rabbit conjunctiva appears to be a moderately tight, fluid-secreting barrier capable of active Cl- transport that is subject to cAMP modulation. Given that the conjunctival epithelium can transdifferentiate into the corneal epithelium under proper conditions, the present proposal seeks to test the hypothesis that the same ion transport processes in the corneal epithelium also exist in the conjunctiva. There are 3 SPECIFIC AIMS in this 3-year proposal: (1) To determine the relative contribution of various ion transport processes to the short-circuit current (Isc) in the pigmented rabbit conjunctiva. The focus will be on Na+/K+ ATPase, Cl- channel, Na+-K+-2Cl- (Na+-Cl-) cotransport, K+ channel, Na+ channel, Na+-glucose cotransport, Na+-amino acid cotransport, and Na+/H+ antiport; (2) To determine the influence of active Cl- secretion and Na+ absorption in water and-paracellular drug transport across the conjunctiva; and (3) To begin elucidating the regulatory mechanisms of Cl transport mediated by Ca2+, PKC, and particularly cAMP. The principal METHODOLOGY includes the measurement of (a) Isc, transmural resistance, and potential difference using the voltage clamp and Ussing chamber assembly; (b) transconjunctival net flux, uptake, and efflux of Na+, K+ (Rb+), and Cl- using a suitable radionuclide in the presence of various inhibitors and activators of ion transport processes; (c) transconjunctival water transport using a macromolecular radiotracer dilution method; and (d) transconjunctival drug transport using mannitol and various FITC-dextrans as paracellular markers. The IMPORTANCE of this research is that it will set the stage for defining the role of ion transport in the regulation of conjunctival cell volume, mucin secretion, as well as electrolyte and fluid balance in the conjunctival microenvironment in health, aging, and various disease states. These diseases may include dry eye, hormonal deficiencies, autoimmune diseases, and inflammation. Further work will reveal how ion transport processes can be exploited through formulation design to maximize drug transport across the conjunctiva for targeting to the posterior segment tissues of the eye.